I have unfortunately never gotten to handle an original, but pictures I have seen show that the majority of old makers followed the contour of the barrel. It makes the gun look more graceful and slender too. I don't believe the old builders did this primarily for aesthetic reasons, but more as a practicality. There was just no reason to leave so much wood on the gun which made it heavier and less well balanced. It could also be that it made the gun easier to keep a grip on, or that it was just more comfortable to hold. I know that once I get a fore stock completed, one of my last tasks in the build, it feels like a long rifle.
I have also noticed from picture that many barrels don't have the side flat half-way embedded in the stock. Rather, there is a bit more of the barrel above the fore stock on the side flats than below it. This also makes the gun look slimmer. After all, there is really no reason for the fore stock at all, because it doesn't support the barrel at all. One reason it may be there is because of muskets being relatively thin barrels, and the thinking may have been that this prevented damage to the barrel. And the full stock could have been a carry-over from that. But this is pure conjecture on my part.
Matt